1. Field of the Invention
The present invention relates to vehicle detectors and vehicle detecting methods and in particular to a vehicle detector and a vehicle detecting method suitable for detecting another vehicle existing in the vicinity of a vehicle.
2. Description of the Related Art
A known vehicle-mounted driving aid apparatus determines the distance between a first vehicle on which the driving aid apparatus itself is mounted (hereinafter also referred to as a host vehicle) and a second vehicle ahead of or behind the first vehicle by detecting the second vehicle using a radar apparatus, so that, if the distance is too short, the driver of the first vehicle is warned or the speed of the first vehicle is restricted to avoid a collision (refer to, for example, Japanese Unexamined Patent Application Publication No. 2003-99762).
The radar apparatus used in such a driving aid apparatus receives reflected electromagnetic waves, such as microwaves or laser beams, emitted toward the second vehicle and detects the second vehicle based on the result of the received reflected waves.
More specifically, if radar reflection points in a radar pattern indicate a low speed relative to the host vehicle and form one group of many reflection points with intensities above a predetermined level, the group of reflection points is regarded as a vehicle, thus discriminating the vehicle from road noise.
However, since reflection points detected by the radar apparatus differ depending on, for example, the radar radiating position in the vehicle, the number of reflection points constituting the detected group is unreliably in some cases.
Furthermore, if a plurality of groups of reflection points exists such that the groups are close to one another, i.e., if the groups of reflection points are too close to one another, two vehicles are mistakenly regarded as one large vehicle.
Thus, the known vehicle-mounted driving aid apparatus has a problem that it is difficult to detect the second vehicle accurately and reliably.